In use, only a small fraction of the radio frequency (RF) energy transmitted by smartphones and other wireless devices is used to communicate with a wireless access point, such as a cellular base station or a wireless network router. This is because small wireless devices, including mobile wireless devices, transmit RF signals in all directions from the device in order to ensure uninterrupted communication, regardless of the orientation of the wireless device.
It would be useful to collect or harvest the unused RF signals in order to convert them, for example, to direct current (DC) power and supplement the capacity of the wireless device battery. However, existing RF energy harvesting designs have been unable to efficiently collect and convert RF signals sent on different frequencies and at different signal strengths without adversely affecting the cellular signal strength and data transmission rates.